Dust extraction installation for blast furnace gas

ABSTRACT

The preliminary cleaning stage for a dust extraction installation for blast furnace gas is comprised of a large-sized cyclone which comprises a vertical pressurized tank. A gas furnace gas line arriving from the blast furnace is connected to an axial delivery device situated at the upper end of the pressurized tank. The delivery device is configured such that it introduces the blast furnace gas into the pressurized tank in an axial direction. A swirl device with guide vanes is positioned below the axial delivery device and causes the blast furnace gas which is axially introduced into the pressurized tank to swirl about the axis of the pressurized tank.

FIELD OF THE INVENTION BACKGROUND OF THE INVENTION

The invention relates to adjust extraction installation for blastfurnace gas.

Dust extraction installations for blast furnace gas generally comprise apreliminary cleaning stage and a fine cleaning stage. The preliminarycleaning stage is formed by a dust catcher. The latter consistsessentially of a large vertical pressure vessel, which is connected tothe blast furnace throat via a gas pipe with a large cross-section. Thegas enters the pressure vessel vertically from the gas pipe, wherein theincrease in cross-section on entry of the gas into the pressure vesselresults in a considerable reduction of its velocity. Consequently atleast the coarsest particles fall vertically from the gas flow beforethe flow leaves the dust catcher at the top end of the pressure vesselafter reversal of direction. The separated particles are collected in adust hopper, from which they are removed via a lock, at the bottom endof the pressure vessel. The pre-cleaned blast furnace gas then passesfrom the dust catcher to the fine cleaning stage, which normallycomprises at least one gas scrubber or electrostatic precipitator.

As the dust catcher achieves poor separation efficiency, the blastfurnace gas can also be passed through a cyclone separator after leavingthe dust catcher and before being passed to the fine cleaning stage. Acyclone separator of this type comprises one or more cyclones connectedin parallel. The latter are pressure vessels, into which the blastfurnace gas is fed tangentially at high speed, with the result that itis set into a swirling motion. The particles are thrown by centrifugalforce to the outer wall of the cyclone separator and slide down thisouter wall into a dust hopper. It is obvious that two-stage preliminarycleaning of this type significantly increases the costs of the dustextraction installation and requires expensive piping on the gas sidefor the connection of the cyclone separators connected in parallel.

A dust extraction installation for blast furnace gas in which the dustcatcher is replaced by a single large cyclone separator has likewisealready been built (dust extraction installation of blast furnace No. 2in the Schwelgen works of THYSSEN Krupp Stahl AG). The main gas pipefrom the blast furnace is introduced tangentially into the cyclonevessel, with the result that the blast furnace gas is set into aswirling motion, so that the dust separation takes place as alreadydescribed above. However, a large cyclone separator of this type has sofar been unable to displace the familiar dust catcher from the market,although there has long been a requirement for more efficientpreliminary cleaning of the blast furnace gas. The chief reasons aremost probably: (1) problematical connection of the gas pipe from theblast furnace throat to the large cyclone separator; (2) reservationsabout wear on the pressure vessel and (3) a lack of empirical valuesconcerning the use of such large cyclone separators for the preliminarycleaning of blast furnace gases. With regard to (1) it should be statedthat the tangential connection of the large blast furnace gas pipe (witha cross-section up to 4 m) to the cyclone vessel requires inter alia acomplicated pipe route, lateral supporting structures requiring a lot ofspace, additional pipe bends and compensators and expensive rectangularducts, which are reinforced against buckling. If an existing dustcatcher is to be replaced by a large cyclone separator, thisnecessitates important modifications to the blast furnace gas pipe andsteel construction. There is often insufficient space for lateralsupporting structures for the gas pipe from the blast furnace throat. Inthis connection it should likewise be pointed out that the support ofthe gas pipe from the blast furnace throat is by no meansunproblematical due to the heavy weight of the pipe (heavy refractorylining), the wind load to be taken into account (large diameter) and thethermal expansion (large length and large temperature differences). Withregard to (2) it should be noted by way of explanation that the gasflowing into the cyclone separator impinges frontally at high speed onthe vessel wall, which leads to heavy wear. With regard to (3) it shouldbe mentioned that the blast furnace operators fear inter alia that thepredicted separation characteristics of the large cyclone separator willnot be observed. As the separation characteristics of a cycloneseparator of this type are determined exclusively by the geometry of thecyclone separator and the tangential gas inflow, it will be appreciatedthat subsequent improvement of the separation characteristics ispossible only at considerable cost.

Therefore, the problem underlying the present invention is to provide adust extraction installation for blast furnace gas with a preliminarycleaning stage, which has a high separation efficiency but does not havethe above-mentioned disadvantages of the known solution with a largecyclone separator as the preliminary cleaning stage, or has thesedisadvantages only to a reduced extent.

SUMMARY OF THE INVENTION

According to the invention this problem is solved by a dust extractioninstallation according to claim 1. A dust extraction installation ofthis type comprises, in a known manner, a preliminary cleaning stage anda fine cleaning stage. The preliminary cleaning stage is formed by alarge cyclone separator, which comprises a vertical pressure vessel,into which a gas pipe from the blast furnace terminates. According tothe invention an axial feed device for the blast furnace gas, to whichthe gas pipe from the blast furnace can be connected, is provided at thetop end of the pressure vessel. This axial feed device is designed insuch a way that it introduces the blast furnace gas into the pressurevessel in an axial direction. A swirl device with guide blades isarranged under the feed device. It is designed in such a way that itcauses the blast furnace gas introduced axially into the pressure vesselto swirl about the axis of the pressure vessel. The particles present inthe blast furnace gas are thrown by the centrifugal force to an outerwall of the pressure vessel and slide down this wall. It should bestated that the axial feed device for the blast furnace gas, compared toa tangential feed device, substantially simplifies the connection of thelarge cyclone separator to the gas pipe from the blast furnace. The pipecan be connected from above to the axial feed device and thus besupported vertically above the cyclone separator. Consequently the notinsignificant support problem is greatly simplified. Separate supportingstructures, additional pipe bends and compensators as well asrectangular ducts reinforced against buckling for a lateral tangentialconnection of the pressure vessel are dispensed with. Furthermore, thewear on the vessel wall in the inflow area is greatly reduced by theaxial introduction of the blast furnace gas. The swirling motion of theblast furnace gas is produced by the guide blades, which can be designedas easily interchangeable wearing parts. The dust extractioninstallation according to the invention thus has the additionaladvantage that the separation characteristics of the installation can beadapted at any time to new requirements by modifications to the guideblades in the swirling device, i.e. at acceptable cost.

The pre-cleaned blast furnace gas could be removed, for example, at thebottom end of the cyclone separator by a central outlet connection pipe.As in most cases the blast furnace gas enters the following finecleaning stage from above, it is however advantageous to remove thepre-cleaned blast furnace gas at the top end of the pressure vesselthrough a central outlet connection pipe. In this case the feed deviceadvantageously has at least two inlet connection pipes aligned upward,which terminate in the pressure vessel around the central outletconnection pipe. The greater the number of inlet connection pipes in thefeed device, the more homogeneous is the inflow to the swirling devicein the pressure vessel. For the connection to the blast furnace gas pipethe feed device advantageously has a distributor outside the pressurevessel. This distributor comprises a connection pipe aligned verticallyupwards and pipe branches aligned downwards. The gas pipe from the blastfurnace is connected to the central connection pipe and the inletconnection pipes of the feed device to the pipe branches. Hence the finecleaning stage can be connected to the central outlet connection pipe ofthe pressure vessel by means of a connecting line, which is led betweentwo adjacent pipe branches of the distributor. The distributor ispreferably designed with axial symmetry.

In the pressure vessel the feed device advantageously has a taperedinlet bell extending downwards, which is traversed by the central outletconnection pipe. An annular gap, in which the swirling device isinstalled, is formed between the bottom edge of the inlet bell and thewall of the pressure vessel. This inlet bell is advantageously supportedby the central outlet connection pipe, so that the pressure vessel andinlet bell can expand independently of each other.

The guide blades are advantageously inserted from outside through slitsin the wall of the pressure vessel into the swirling device, so thatthey can be changed relatively easily. In an advantageous embodimenteach of the guide blades has at its outer end a mounting plate, which isscrewed with a seal on to a flange which encloses the corresponding slitin the wall of the pressure vessel. The inner end of a guide blade canbe introduced into a slit-type recess in the bottom edge of the inletbell in order to keep the gas flow passing the swirling device as smallas possible.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplified embodiment of the invention will now be described belowwith reference to the enclosed figures, wherein:

FIG. 1: is an elevation, which is partially drawn as a section, of apreliminary cleaning stage of a dust extraction installation for blastfurnace gas according to the invention;

FIG. 2: is an elevation as in FIG. 1, but offset by 90°;

FIG. 3: is a section of a swirling device;

FIG. 4: is a perspective view, partially as a section, of the swirlingdevice according to FIG. 3; and

FIG. 5: is an elevation, which is partially drawn as a section, of apreliminary cleaning stage as in FIG. 1, a large cyclone separator beinginstalled in an existing dust catcher.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preliminary stage of a dust extraction installation forblast-furnace gas according to the invention shown in FIGS. 1 and 2 isformed by a large cyclone separator, which is designated 10. Theblast-furnace gas to be cleaned is fed to the preliminary cleaning stagevia a blast furnace gas pipe 12, which comes directly from the blastfurnace throat (not shown).

The large cyclone separator 10 comprises a vertical cylindrical pressurevessel 14. The bottom end of the pressure vessel 14 forms a dust hopper16, which can be emptied in a known way via a lock unit 18. FIG. 2 showse.g. the emptying of the lock unit 18 via a chute 20 into a rail wagon.

The top end of the pressure vessel 14 is shown as a section in FIGS. 1and 2. It is sealed gastight by a dome-type hood 24. As shown in FIG. 2,this hood 24 has two peripheral inlet connection pipes 26, 28, which arearranged symmetrically with the central axis 30 of the pressure vessel14. The angle a between the central axis 30 of the pressure vessel 14and the central axis 32 of an inlet connection pipe 26 is about 30°.

An axially symmetrical distributor is designated 34 in FIG. 1 (the axisof symmetry of the distributor is the axis 30). This distributor 34 isshaped like a Y-pipe. It has two pipe branches 36, 38, which extenddownwards and with which it is connected to the two inlet connectionpipes 26, 28 of the dome-type hood 24, as well as a connection pipe 40extending vertically upwards. The latter is connected via a compensator42 and if necessary a shut-off valve 44 to the blast furnace gas pipe12. It should be noted that the blast furnace gas pipe 12 restsvertically on an upper supporting framework 46, which in turn rests on alower supporting framework 48, which carries the large cyclone separator10 or is supported laterally at its top end. However, it is notprecluded that the blast furnace gas pipe 12 can directly restvertically on the pressure vessel 14.

The blast furnace gas is introduced essentially axially into thepressure vessel 14 via the connection pipes 26, 28. It encounters herean inlet bell 50 expanding downwards, which is arranged centrally in thepressure vessel 14 in such a way that an annular gap 56 is formedbetween the bottom edge 52 of the inlet bell 50 and the wall 54 of thepressure vessel. A swirling device 58, the construction of which isdescribed below, is arranged in this annular gap 56.

The swirling device 58 causes the blast furnace gas introduced axiallyinto the annular gap 56 to swirl about the axis 30 of the pressurevessel 14. The particles in the blast furnace gas are thrown against thecylindrical outer wall 54 of the pressure vessel 14 by the centrifugalforce and slide down this outer wall 54. They reach the alreadydescribed dust hopper 16 here. At a bottom deflector bell 59 the gasflow is again diverted upwards, where it terminates under the inlet bell50 in a central outlet connection pipe 60, which is arranged coaxiallywith the central axis 30 of the pressure vessel. The inlet bell 50 istraversed by the central outlet connection pipe 60 with a gastight sealand is also supported exclusively by this connection pipe. The domedhood 24 is likewise traversed by the central outlet connection pipe 60,the latter being led gastight, but at the same time with axialmovability through a pipe connection pipe 62 installed in the domed hood24, so that the outlet connection pipe 60 can expand freely in relationto the domed hood 24 (see FIG. 2). As likewise shown in FIG. 2, thecentral outlet connection pipe 60 is connected above the domed hood to agas pipe 64, which conveys the pre-cleaned blast-furnace gas to the finecleaning stage (not shown). This gas pipe 64 coming from above is ledbetween the two pipe branches 36, 38 of the distributor 34.

The swirling device 58 will now be described in more detail withreference to FIGS. 3 and 4. It comprises a large number (e.g. 30) ofguide blades 66, which have an overlap of about 20 to 40% and an angleof incidence d of 15 to 30°. Each of the guide blades 66 is insertedfrom outside through a slit 68 in the wall 54 of the pressure vessel 14into the swirling device 58. These slits 68 are each enclosed on theoutside of the wall 54 by a frame 70, which carries a flange 72. Theguide blades 66 each comprise a blade 74, which may be flat or curved,and a mounting plate 76, which is screwed gastight on the flange 72. Theblade 74 projects in a cantilevered way from the mounting plate 76 intothe pressure vessel 14. The inner end of each blade 74 can be introducedwith play all round into a slit-type recess 78 of a wear lining 79 ofthe bottom edge 52 of the inlet bell 50. However, there is no fixedmechanical connection between the guide blades 66 and the inlet bell 50,so that the latter can expand freely in relation to the pressure vessel14. The blades 74, the wall 54, the inlet bell 50, the deflector bell 59and all other parts which are exposed to heavy abrasion by the blastfurnace dust in the cyclone separator 10 are, of course, provided with awear lining 79 consisting e.g. of a ceramic material.

An important advantage of the swirling device 58 is that the blades 66can be changed individually from outside. They can, in fact, easily bewithdrawn from the pressure vessel 14 or pushed into the latter from anouter platform 80. Guide webs 82 on the blade 74 facilitate the mountingof the guide blades 66 by centering the blade 74 in the frame 70.Finally, it should be noted that with an adequately large slit 68 in thewall 54 even guide blades 66 with a different angle of incidence δ, adifferent overlap and/or a different curvature can be used. This meansinter alia that the separation characteristics of the cyclone separator10 can be subsequently changed at an acceptable cost. For example, ablast furnace operator wishing to reduce the zinc or lead content in thedust from the preliminary cleaning stage can have the swirling device 58redesigned in such a way that the cyclone separator has a lowerseparation limit of about 16 mm particle size. The dust extractioninstallation described thus opens up new possibilities to the blastfurnace operator for optimisation of dust extraction from the blastfurnace gases.

FIG. 5 shows an interesting possibility for renovation according to theinvention of the preliminary cleaning stage of an existing dustextraction installation with an old dust catcher 100. The large cycloneseparator 10′, which is essentially identical to the large cycloneseparator 10 in FIGS. 1 to 4, is inserted axially in the truncatedpressure vessel 102 of the dust catcher 100, from which all fittingshave been removed in advance. Only the head end 104 of the large cycloneseparator 10′ projects from the pressure vessel 102. It is connected tothe top edge of the truncated pressure vessel 102 by means of a gastightconnection 106. By contrast the lower part of the large cycloneseparator 10′ projects axially into the pressure vessel 102 and at itsbase end has an opening 108 into a dust hopper 116. The latter is formedby the dust hopper of the old dust catcher 100. The supportingconstruction 110 for the gas pipe 112 coming from the blast furnacethroat is supported by the pressure vessel 102 of the dust catcher 100.This embodiment has the important advantage that the old dust catcherneed not be fully dismantled and that the modifications to the steelconstruction or gas pipes can be restricted to a minimum.

What is claimed is:
 1. A dust extraction installation for blast furnacegas comprising: a preliminary cleaning stage formed by a large cycloneseparator and connected to a blast furnace gas pipe coming from a blastfurnace; and a fine cleaning stage arranged downstream of saidpreliminary cleaning stage; wherein said large cyclone separatorincludes: a vertical pressure vessel having a top end, a bottom end, acentral vertical axis and a lateral wall; a feed device at said top endincluding a conical inlet bell, which expands downwards towards a bottomedge, so that an annular gap is defined between said bottom edge of saidconical inlet bell and said lateral wall of said pressure vessel, saidfeed device being designed so that said blast furnace gas pipe can beconnected to said feed device from above and so that said feed devicefeeds the blast furnace gas in an axial direction into said annular gap;and a swirling device with guide blades arranged in said annular gap,said swirling device being designed so that the blast furnace gas, whichis axially fed into said annular gap, is subjected to a swirlingmovement about said central vertical axis of said pressure vessel. 2.The dust extraction installation according to claim 1, wherein saidguide blades are inserted into said swirling device from outside throughslits in said lateral wall of said pressure vessel.
 3. The dustextraction installation according to claim 2, wherein: each of saidslits in said pressure vessel is surrounded by a flange; each of saidguide blades has an outer end, an inner end and a mounting plate fixedto its outer end; and said mounting plate is sealingly screwed on tosaid flange.
 4. The dust extraction installation according to claim 3,wherein: said inner end of guide blade is introduced into slit-typerecess in said bottom edge of said inlet bell with play all around saidinner end of a guide blade in said slit-type recess.
 5. A dustextraction installation for blast furnace gas comprising: a preliminarycleaning stage formed by a large cyclone separator and connected to ablast furnace gas pipe coming from a blast furnace; and a fine cleaningstage arranged downstream of said preliminary cleaning stage: whereinsaid large cyclone separator includes: a vertical pressure vessel havinga top end, a bottom end and a central vertical axis, said verticalpressure vessel including a central outlet connection pipe emergingthrough said top end; a feed device at said top end, said feed deviceincluding at least two upwardly projecting inlet connection pipes, whichenter into said pressure vessel around said central outlet connectionpipe and are designed so that said blast furnace gas pipe can beconnected to said feed device from above, whereby said feed device feedsthe blast furnace gas in an axial direction into said pressure vessel;and a swirling device with guide blades arranged below said axial feeddevice, said swirling device being designed so that the blast furnacegas, which is axially fed into said pressure vessel, is subjected to aswirling movement about said central vertical axis of said pressurevessel.
 6. The dust extraction installation according to claim 5,wherein: said feed device comprises a distributor outside said pressurevessel; said distributor has a vertical connection pipe projectingupwardly and downwardly projecting pipe branches; said blast furnace gaspipe is connected to said vertical connection pipe; said inletconnection pipes of said feed device are connected to said pipebranches; and a connecting line connecting said central outletconnection pipe to said fine cleaning stage is led between two of saidpipe branches.
 7. The dust extraction installation according to claim 6,wherein said distributor is designed with axial symmetry.
 8. The dustextraction installation according to claim 5, wherein: said pressurevessel includes a lateral wall; said feed device includes in saidpressure vessel a conical inlet bell, which expands downwards towards abottom edge; said conical inlet bell is axially traversed by saidcentral outlet connection pipe; an annular gap is defined between saidbottom edge of said conical inlet bell and said lateral wall of saidpressure vessel; and said swirling device is arranged in said annulargap.
 9. The dust extraction installation according to claim 8, whereinsaid inlet bell is supported by said central outlet connection pipe. 10.The dust extraction installation according to claim 8, wherein saidguide blades are inserted into said swirling device from outside throughslits in said lateral wall of said pressure vessel.
 11. The dustextraction installation according to claim 10, wherein: each of saidslits in said lateral wall of said pressure vessel is surrounded by aflange; each of said guide blades has an outer end, an inner end and amounting plate fixed to its outer end; and said mounting plate issealingly screwed on to said flange.
 12. The dust extractioninstallation according to claim 11, wherein: said inner end of a guideblade is introduced into a slit-type recess in said bottom edge of saidinlet bell.
 13. A dust extraction installation for blast furnace gascomprising: a preliminary cleaning stage formed by a large cycloneseparator axially inserted into a truncated pressure vessel of an olddust catcher and connected to a blast furnace gas pipe coming from ablast furnace, said large cyclone separator including: a verticalpressure vessel having a top end, a bottom end and a central verticalaxis; a feed device at said top end, said feed device being designed sothat said blast furnace gas pipe can be connected to said feed devicefrom above and so that said feed device feeds the blast furnace gas inan axial direction into said pressure vessel; and a swirling device withguide blades arranged below said axial feed device, said swirling devicebeing designed so that the blast furnace gas, which is axially fed intosaid pressure vessel, is subjected to a swirling movement about saidcentral vertical axis of said pressure vessel.
 14. The dust extractioninstallation according to claim 13, wherein: said truncated pressurevessel has a top edge; said large cyclone separator is inserted in saidtruncated pressure vessel of said old dust catcher so that its top endprojects over said top edge of said truncated pressure vessel; and saidtop end of said large cyclone separator is connected to said top edge ofsaid truncated pressure vessel by means of a gastight connection means.15. The dust extraction installation according to claim 14, wherein:said preliminary cleaning stage further includes a dust hopper of saidold dust catcher; and said large cyclone separator has at its bottom endan opening into said dust hopper.